Structural Constraints, Spandrels, and Exaptation 1263
This argument about the nonadaptive nature of the clitoral site (as advanced by
Symons, 1979; and Gould, 1987a) has been widely misunderstood as a denial of
either the adaptive value of female orgasm in general, or even as a claim that female
orgasms lack significance in some broader sense. Only a grossly overextended
commitment to exclusivity for the simplest form of adaptationist argument could ever
have led to such foolish misunderstanding. I cannot speak from direct experience of
course, but I accept the clear testimony that clitoral orgasm plays a pleasurable and
central role in female sexuality and its joys. All these favorable attributes, however,
emerge just as clearly and just as easily, whether the clitoral site of orgasm arose as a
spandrel or an adaptation. (As a spandrel, the clitoral site would represent the
different expression of a male adaptation, just as male nipples may be the spandrels
of a female adaptation.) After all, we defined the concept of spandrels largely in
terms of their rich potential for exaptive utility (Gould and Vrba, 1982). To state
Nietzsche's principle in another way: origin as a spandrel implies no diminution of
potential for crucial and joyous exaptive use later on.
As to the important question of a potentially adaptive nature for female orgasm
in general, I have no firm opinion, and certainly feel no hostility towards functional
hypotheses in conventional Darwinian terms of enhanced reproductive success. (I
have only questioned the adaptive interpretation of the specifically clitoral site, since
basic developmental anatomy would seem to dictate such a placement for other, and
prior, reasons. Alfred Kinsey (1953), a very fine evolutionary entomologist who
achieved far greater fame in his "second career" as a sociologist of sexual behavior,
upbraided Freud, who had begun his own professional life as a comparative anatomist
(with a doctoral thesis on the neurology of amphioxus), for failing to draw the
obvious inference from a developmental homology that he knew perfectly well, and
from easily available information about the rich innervation of the clitoris, and the
virtual anesthesia of the vaginal canal.
Some common hypotheses for the adaptive nature of female orgasm have not
fared well, including the standard argument that muscular contractions during orgasm
help to draw sperm down the vaginal canal towards the site of fertilization (see Buss
et al., 1998). Other arguments of a more psychological nature, especially the claim
that orgasm may have positive value in stimulating pair bonding, make more sense in
a too obvious way that always manages to incite my skepticism. In any case, the
establishment of an important and potentially exaptive value of female orgasm does
not challenge the hypothesis that the clitoral site originated as a nonadaptive spandrel
(in Darwinian terms for enhancing reproductive success, not in human terms of
female pleasure) of selection upon the homologous organ in males, the penis.
RELATIONSHIP TO COMPLEXITY. As a primary correlation regulating the
distribution and importance of spandrels vs. primary adaptations, increasing
complexity of an organ must imply a rising relative frequency of nonadaptive side
consequences with potential future utility. With greater complexity in number and
form of components, cooptable side consequences must rise to